PSI - Issue 13

Jacopo Schieppati et al. / Procedia Structural Integrity 13 (2018) 642–647 Schieppati et al. / Structural Integrity Procedia 00 (2018) 000 – 000

645

4

(b)

(a)

30

30

28

28

26

22 Temperature T , °C 24

26

22 Temperature T , °C 24

0 10 20 30 40 50 60 70 80 90 100 20

20

0

10000 20000 30000 40000 50000 60000

Crack length c , mm

Number of cycle N , cycle

Fig. 1. (a) Surface temperature as a function of number of cycle and (b) surface temperature as a function of crack length. The plots refer to a test carried out at 4 Hz; the grey area corresponds to the number of cycle (a) and the position (b) at which the crack was below the IR sensor.

(a)

32

10 -1

30

10 -2

28

10 2 Crack growth rate dc/dN , mm/cycle 10 -5 10 -4 10 -3

20 Temperature T , °C 22 24 26

0.25 Hz 1 Hz 4 Hz 10 Hz

0.25 Hz 1 Hz 4 Hz 10 Hz

18

0

1000 2000 3000 4000 5000

10 3

10 4

Number of cycle N, cycle Tearing energy G , J/m 2 Fig. 2. (a) Surface temperature as a function of number of cycle and (b) crack growth rate as a function of tearing energy at different frequencies.

(a)

(b)

(b)

90

1400

0,25 Hz 1 Hz 4 Hz 10 Hz

85

1200

80

1000

75

800

Energy U , %

70

Load F , N

600

25

400

20

U sto U diss

15

200

10

0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4 0

10 3

10 4

10 5

Number of cycles N , cycle

Displacement s , mm

Lake and Lindley (1964) and Lindley (1974) reported that the fatigue crack growth rate is related to a static growth and a dynamic growth component, which are additive. The first component is related to the viscoelastic effect and connected to the time necessary for completing one cycle, i.e. the reciprocal of the frequency, while the dynamic Fig. 3. Energy evaluation from crack growth experiments at different frequencies: (a) hysteresis loops recorded at 1000 cycles; (b) percentage of dissipated energy (full line) and elastically stored energy (dashed line) as a function of the number of cycle.